This invention is in the field of cooking of foods, and more specifically the invention is concerned with browning and cooking of foods in such a way as to avoid the exhausting to the atmosphere of objectionable smoke and gases from rendered fats and other products, and in a fast and efficient manner which greatly reduces space requirements as well as cleaning requirements. The invention is also concerned with reclaiming of heat from various processes including both cooking and incineration of rendered fats and oils, for use in other processes associated with the system.
Cooking systems, including commercial ovens, often have a problem with exhausting of gases and smoke particles from rendered fats, oils and other materials emanating from the cooked food product. Environmental regulations have required scrubbers or smoke afterburners associated with exhaust stacks, to make the gases and remaining particles suitable for introduction to the atmosphere.
Radiant heat in ovens is well known and has been used both commercially and in home ovens. Calrod and gas infra-red heaters are often used as cooking elements.
A cooking and browning system is described in Forney U.S. Pat. No. 4,737,373. High temperature, high velocity air is used in an oven to brown a meat, poultry or other food product; separately, before or after the browning step, the food product is cooked at a lower temperature and more slowly, such as in a steam oven on a continuous flow basis. Steam for the slow cook is generated by using exhausted hot air from the browning oven as a source of heat.
Various types of cooking and/or browning ovens are shown in the following U.S. Pat. Nos.: Hoffman et al. 2,529,253, Szabrak et al. 3,721,178, Fagerstrom et al. 3,908,533, Brown 4,023,007, Baker et al. 4,121,509, Lang-Ree et al. 4,254,697, Williams 4,383,823, Wells 4,448,117, Wells et al. 4,473,004, Wiggins et al. 4,569,658, Henke 4,591,333, Hwang et al. 4,834,063, Wells et al. 4,884,552, Baker 4,936,286 and Smith 4,876,426.
Of the above patents, Wells U.S. Pat. No. 4,473,004 discloses a tunnel-type oven which utilizes radiant heat generated from combustion of gas circulated in a closed cylindrical chamber surrounding a food product conveyor, so as to cook products as they advance on the conveyor through the tunnel oven (see particularly FIG. 16). This patent mentions the use of wall temperatures in the range of 1000.degree. to 1200.degree. F. or higher. Because of this high temperature, the patent states that the disclosed ovens can be self-cleaning, with rendered grease droppings, food residue and other food material reduced to ash. The patent also suggests the desirability of avoiding direct flame contact with food products, to prevent the generation of carcinogens.
Wells U.S. Pat. No. 4,884,552 discloses another form of gas-fired tunnel oven.
The Wigging patent describes a tunnel oven of the convective type in which off gases from cooking are directed through a heat exchanger for heat exchange with ambient air before being circulated into the oven, and the patent mentions an increase in efficiency of the oven due to this heat exchange.
A problem with many commercial ovens, and even domestic cooking facilities, is the direct exposure of products of combustion to the food product being cooked, whether the food contact is by a direct open flame (recognized by Wells to be undesirable) or by gases produced by combustion. This can introduce carcinogens and other undesirable substances into food for human consumption.
None of the above patents has disclosed an oven for cooking and/or browning with the advantages of low emissions and efficiently controlled cooking, in an oxygen-deficient oven atmosphere as in the invention described below.